US20050220588A1 - Forklifts - Google Patents

Forklifts Download PDF

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Publication number
US20050220588A1
US20050220588A1 US10/989,552 US98955204A US2005220588A1 US 20050220588 A1 US20050220588 A1 US 20050220588A1 US 98955204 A US98955204 A US 98955204A US 2005220588 A1 US2005220588 A1 US 2005220588A1
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United States
Prior art keywords
boom
extendable boom
ram
extendable
upright
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US10/989,552
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English (en)
Inventor
Kevin Turnbull
Barry McGrane
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Moffett Research and Development Ltd
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Moffett Research and Development Ltd
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Assigned to MOFFETT RESEARCH AND DEVELOPMENT LIMITED reassignment MOFFETT RESEARCH AND DEVELOPMENT LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MCGRANE, BARRY, TURNBULL, KEVIN
Publication of US20050220588A1 publication Critical patent/US20050220588A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/07563—Fork-lift trucks adapted to be carried by transport vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/065—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks non-masted

Definitions

  • This invention relates to forklifts and in particular to forklift trucks of the type for mounting on the rear of a carrying vehicle, the forklift truck comprising a unshaped chassis having a rear crossbar and pair of side plates mounted at the ends of the rear crossbar and projecting forwardly therefrom, a wheel located adjacent the front of each of the side plates, a steerable rear wheel located centrally on the rear crossbar, a driver's station positioned to one side of the chassis and a motive power unit positioned on the opposite side of the chassis, the forklift truck further comprising a lifting assembly mounted on the chassis.
  • the invention relates particularly to the mast assembly.
  • Truck mounted forklifts otherwise referred to as piggyback forklifts have been known for many years. These piggyback forklifts may be transported to and from the premises of customers of the forklift owner on the back of an articulated truck chassis or trailer and are then used to load or unload goods to or from the trailer on those premises. Typically, these piggyback forklifts are necessarily lightweight and highly manoeuverable and must be able to travel over uneven terrain without difficulty. These piggyback forklifts are not to be confused with other more general application forklifts as there are numerous problems and design constraints applicable to truck mounted forklifts that do not strictly apply to other types of forklift trucks.
  • the known piggyback forklifts can be further categorized into two distinct types of forklifts, vertical mast forklifts and telescopic boom forklifts.
  • Vertical mast forklifts typically comprise a standard lightweight mast that allows for compact storage when mounted on the back of a carrying vehicle as well as reliable performance. In addition to this, the vertical mast forklifts are recognised as being highly stable and easily manoeuverable.
  • Telescopic boom forklifts typically comprise a telescopic boom pivotally mounted adjacent and above the rear wheel of the forklift intermediate the driver's station and an engine unit. These telescopic forklifts have the advantage that the operators view from the driver's station is not obstructed by a vertical mast and by having a telescopic boom they have improved reach capabilities.
  • One of the main problems associated with telescopic boom type piggyback forklifts is that when they are manoeuvering without a load the majority of the weight is concentrated at the back of the piggyback forklift over the back wheel where the telescopic boom is mounted. Having this concentration of weight towards the back wheel in a three wheeled vehicle causes problems in the lateral stability and hence manoeuverability of the piggyback forklift.
  • the piggyback forklift will have a tendency to tilt to one side particularly if subjected to any sudden sharp turns when not carrying a load. This can often cause damage to the piggyback forklift undercarriage as well as exert undesirable pressure on the rear wheel.
  • any tilting of the piggyback forklift can also lead to safety risks to the operator or personnel nearby.
  • the piggyback forklift In order to avoid any possibility of tilting, the piggyback forklift must be manoeuvered at lower speeds than the operator would normally wish thereby slowing down any loading or unloading procedure. Again, this is undesirable as it diminishes the usefulness of the piggyback forklift.
  • piggyback forklifts having telescopic booms Another problem associated with piggyback forklifts having telescopic booms is that the piggyback forklifts, when in the process of being mounted or dismounted from a carrying vehicle move towards or away from the carrying vehicle in an arc rather than directly upwards and downwards as in the case of a vertical mast piggyback forklift. This arcuate movement puts unacceptable pressure on the telescopic arm components and can result in significant wear and tear to the arm components which can ultimately lead to premature failure of the telescopic arm.
  • the present invention is directed towards providing a forklift truck for mounting on the rear of a carrying vehicle that overcomes at least some of the problems associated with the known piggyback forklift trucks that is simple, reliable and efficient to use.
  • a piggyback forklift truck for mounting on the rear of a carrying vehicle comprising a unshaped chassis having a rear crossbar and a pair of side plates, each of the side plates being connected to one end of the rear crossbar and projecting forwardly therefrom.
  • a ground engaging wheel is mounted adjacent the forwardmost end of each of the side plates and a steerable rear wheel is mounted centrally on the rear crossbar.
  • a driver's station is mounted to one side of the chassis and a motive power unit is mounted on the other side of the chassis.
  • the piggyback forklift further comprises a lifting assembly mounted on the chassis, the lifting assembly comprising a carriage slidably mounted on the chassis, the carriage being slidable towards and away from the rear crossbar and means to move the carriage back and forth along the chassis.
  • the lifting assembly further comprises an upright boom support mounted on the carriage and an extendable boom pivotally mounted adjacent its proximal end on the boom support adjacent the uppermost end of the boom support.
  • a fork carrier carrying forks is mounted on the distal end of the extendable boom and there is provided means to pivot the boom about the pivot point on the upright boom support.
  • Another advantage of this type of piggyback forklift is that the entire lifting assembly may be moved forward on the forklift chassis relative the rear crossbar so that the lifting assembly is located adjacent the front wheels of the forklift. This is particularly useful when the piggyback forklift is being operated without a load on the forks. With the weight of the lifting assembly displaced towards the front of the piggyback forklift a more even weight distribution across the piggyback forklift is achieved. This will enhance the stability and hence manoeuverability of the piggyback forklift and will reduce any tendency of the piggyback forklift to tilt while in motion.
  • a further advantage of the piggyback forklift truck of the present invention is that the reach of the piggyback forklift will be improved particularly when loading or unloading goods from an elevated position when compared with standard telescopic boom piggyback forklift trucks.
  • the upright boom support and the extendable boom are dimensioned to allow the boom to pivot to and from a closed position whereby the boom is substantially orthogonal to the ground and an open position whereby the free end of the boom point upwards and away from the ground.
  • an extendible boom that may pivot to a closed position facing substantially vertically downwards, the loading and unloading of the piggyback forklift truck is further simplified and the wear and tear on the boom components is reduced.
  • the piggyback forklift truck may be mounted onto a carrying vehicle when the extendible boom is in this position by inserting the forks into receiving sockets on the carrying vehicle in the known manner and thereafter the forks can be lowered in a vertical direction which will raise the piggyback forklift upwards relative the carrying vehicle.
  • the piggyback forklift will not have to be mounted onto the carrying vehicle in a wide arc as is the case with other known piggyback forklifts having telescopic booms.
  • This facility of X-Y movement offered by the boom configuration allows for much simpler operator machine manipulation during truck mounting and maintains a standard method which will allow pressure relieving facilities to be installed.
  • the upright boom support further comprises a pair of spaced apart upright support arms, the extendable boom being pivotally mounted therebetween and nestable within the spaced apart upright support arms when in a closed position.
  • This configuration will allow the extendable boom to nest within the arms thereby allowing the extendable boom to face directly downwards orthogonal to the ground. This will facilitate loading and functionality of the piggyback forklift.
  • the extendable boom is pivotally mounted on the upright boom support by way of a pivot joint, the pivot joint comprising a pair of pivot arms protruding outwardly from one of the extendable boom and the upright boom support so that the extendable boom may pivot to a closed position with the boom substantially parallel to the upright boom support.
  • pivot arms will space the main body portions of the extendable boom and the upright boom support apart thereby allowing the boom to pivot downwardly until it is substantially parallel with the upright boom support.
  • the pivot arms could of course be on either the upright boom support protruding forwardly of the boom support or on the extendable boom protruding rearwards and orthogonally to the main longitudinal axis of the extendable boom.
  • one pivot arm could be provided on the upright boom support and the other pivot arm could be provided on the extendable boom.
  • the extendable boom and the upright boom support are held spaced apart by the pivot arms to such an extent that the boom can pivot to a position substantially parallel to the upright boom support thereby allowing vertical lift of the piggyback forklift which in turn has benefits for the loading process as well as the functionality of the piggyback forklift.
  • the boom comprises a two part boom having an inner casing and an outer casing, the inner casing being slidably mounted with respect to the outer casing.
  • the outer casing is pivotally mounted on the upright boom support and the inner casing is slidable with respect to the outer casing.
  • a boom extension ram is connected at one of its ends to the inner casing and at its other end to the outer casing to cause sliding movement of the inner casing relative the outer casing.
  • a hydraulic lift ram is provided to cause the extendable boom to pivot relative the upright boom support, the hydraulic lift ram being connected at one end to the carriage and at its other end to the boom.
  • a pair of lift rams each of the lift rams being connected at one of their ends to the carriage and at their other end to the boom, one of the pair of lift rams being a high pressure lift ram and the other lift ram being a low pressure lift ram.
  • a compensating jack is mounted on the boom, one end of the compensating jack being connected to the boom and the other end of the compensating jack being coupled to the fork carrier. Means to sequence the compensating jack fluid supply with the fluid supply of the lift ram are also provided as well as means to transfer excess fluid pressure from the compensating jack to the high pressure lift ram.
  • the compensating jack further comprises a compensating ram and a tilt ram, the tilt ram being operable to tilt the forks upwards or downwards with respect to the horizontal longitudinal axes.
  • the tilt ram further comprises a tilt ram cylinder having an internal bore and tilt ram piston partially housed therein
  • the compensating ram further comprises a compensating ram cylinder having an internal bore and a compensating piston partially housed therein, the internal bore of the tilt ram cylinder being greater in diameter than the internal bore of the compensating ram cylinder.
  • the tilt ram and the compensating ram are connected together in an end to end fashion, the end of the compensating ram cylinder being connected to the end of the tilt ram cylinder.
  • the compensating jack is coupled to the fork carrier by way of a linkage mechanism, the linkage mechanism comprising a pair of elongate link arms, each of the elongate link arms being pivotally connected at one end to the compensating jack and pivotally connected at the other end to the fork carrier spaced apart from each other, one of the link arms being arcuate in shape.
  • the forces could have been directed at almost right angles to the compensating jack which greatly inhibited the operation of the compensating jack and furthermore exerted large forces on the compensating jack causing the compensating jack to fail to operate and in come cases resulting in failure of the compensating jack altogether.
  • the linkage mechanism allows the compensating jack to operate under significantly less forces than before which allows a more lightweight compensating jack to be used.
  • the compensating jack is housed internal the boom. There is additionally provided a side shift mechanism mounted intermediate the forks and the fork carriage to provide lateral movement of the forks relative the longitudinal axis of the forklift. Friction reducing means such as nylon pads or ball bearings are provided intermediate the inner and the outer casings.
  • a piggyback forklift truck in which the extendable boom further comprises a telescopic boom having a plurality of boom components nested together. This is seen as a useful alternative construction of extendible boom that will be compact and efficient to use.
  • a piggyback forklift truck in which the extendable boom is pivotable to a closed position in which the boom is at an angle of between ⁇ 3° of the orthogonal with respect to the ground.
  • the carriage is further provided with a plurality of rollers and each of the side plates is further provided with a track for reception of at least one carriage roller, the carriage sliding forwards and backwards on the chassis relative the rear crossbar along the rollers in the tracks.
  • the tracks may be formed integrally with the side plates for maximum rigidity of the entire assembly or alternatively they can be provided separately and attached to the side plates of the chassis.
  • the main advantage of the present invention is that the piggyback forklift will have improved reach capabilities without having to provide additional pantograph or roller arrangements for the forks and furthermore, the piggyback forklift will have increased stability when manoeuvering due to the centre of gravity being displaced forwardly on the vehicle.
  • FIG. 1 is a front perspective view of a piggyback forklift according to the invention with the extendable boom in a closed fully extended configuration;
  • FIG. 2 is a front perspective view of the piggyback forklift of FIG. 1 with the extendable boom in a closed fully retracted configuration;
  • FIG. 3 is a front perspective view of the piggyback forklift of FIG. 1 with the extendable boom raised and fully retracted;
  • FIG. 4 is a front perspective view of the piggyback forklift of FIG. 1 with the carriage moved forward on the chassis relative the rear crossbar and the extendable boom raised and fully extended:
  • FIG. 5 is a front perspective view of the piggyback forklift of FIG. 1 with the carriage moved forwards on the chassis relative the rear crossbar and the extendable boom in an open fully extended configuration;
  • FIG. 6 is a front perspective view of the piggyback forklift of FIG. 1 with the carriage moved forwards on the chassis relative the rear crossbar and the boom in a closed fully extended configuration;
  • FIGS. 7 ( a ) to FIG. 7 ( g ) are side views of the piggyback forklift according to the invention carrying a load with the carriage and extendable boom in various different configurations;
  • FIGS. 8 ( a ) to FIG. 8 ( d ) inclusive are side views of a piggyback forklift according to the invention being mounted onto a carrying vehicle;
  • FIG. 9 is a side view of a truck mounted forklift according to the invention gripping a “near side” load
  • FIG. 10 is a side view of the truck mounted forklift according to the invention gripping a “far side” load
  • FIG. 11 is a front perspective view of a lifting assembly for use with a piggyback forklift according to the invention.
  • FIG. 12 is a rear perspective view of the lifting assembly of FIG. 11 ;
  • FIG. 13 is a side cross-sectional view of the lifting assembly of FIGS. 11 and 12 ;
  • FIG. 14 ( a ) and FIG. 14 ( b ) are side views of the linkage mechanism used with the lifting assembly according to the invention with the fork carrier at different angles of tilt relative the boom;
  • FIG. 15 ( a ) and FIG. 15 ( b ) are side views of a standard linkage mechanism with the fork carrier at different angles of tilt relative the boom;
  • FIGS. 16 ( a ) to FIG. 16 ( d ) are schematic representations of the various hydraulic rams operable on the lifting assembly and the flow of fluid therebetween;
  • FIG. 17 is a stability triangle diagram comparing the centre of gravity of an unloaded piggyback forklift of the present invention to the centre of gravity of a known unloaded telescopic boom piggyback forklift.
  • FIGS. 1 to 6 there is shown a piggyback forklift truck 1 for mounting on the rear of a carrying vehicle comprising a u-shaped chassis 3 having a rear cross member 5 and a pair of side plates 7 mounted at the ends of the rear cross member 5 and projecting forwardly therefrom.
  • a wheel 9 is located adjacent the front of each of the side plates and a steerable rear wheel 11 is located centrally on the rear cross member.
  • a driver's station 13 and a motive unit 15 are mounted on opposite sides of the chassis relative to each other and there is further provided a lifting assembly, indicated generally by the reference numeral 17 .
  • the lifting assembly 17 further comprises a carriage 19 slidably mounted on and moveable forwards and backwards relative the rear crossbar along the side plates and an upright boom support 21 mounted atop the carriage and projecting upwardly therefrom, an extendible boom 23 is pivotally mounted adjacent its proximal end on the boom support adjacent to the uppermost end of the boom support and has a fork carrier 25 mounted on the distal end of the extendable boom carrying a pair of lifting forks 27 thereon.
  • the carriage is provided with rollers (not shown) which are mounted in tracks 29 , only one of which is shown, on the side plates and there is provided means to move the carriage (not shown) forwards and backwards along the tracks on the side plates.
  • FIGS. 3 to 5 inclusive there is shown means to pivot the boom about its mounting provided by a pair of lift rams 31 , 33 , which are mounted at one end to the carriage and at their other end to the boom. Extension of the lift rams 31 , 33 will cause the boom to pivot upwardly from a closed configuration with the boom facing substantially vertically downwards and substantially orthogonal to the ground to an open configuration in which the boom faces outwardly and upwardly away from the upright boom support.
  • the extendible boom 23 further comprises a two part boom having an outer casing 35 pivotally mounted to the boom support and an inner casing 37 slidably mounted with respect to the outer casing and retained therein.
  • An elongate hydraulic extension ram 39 is provided and connected at one end to the outer casing and at its other end to the inner casing. Operation of the extension ram 39 will cause extension or retraction of the inner casing relative the outer casing. Nylon pads (not shown) are provided intermediate the inner and outer casings to prevent excessive wear and tear and to facilitate movement between the outer and inner casings.
  • the upright boom support further comprises a pair of spaced apart upright support arms, 22 a , and 22 b .
  • the extendable boom further comprises a pivot joint which in turn comprises a pair of pivot arms 24 a , 24 b and is pivotally mounted to the spaced apart upright support arms 22 a , 22 b by way of the pivot arms 24 a , and 24 b .
  • the extendable boom 23 may pivot about the pivot arms on the spaced apart upright support arms from a fully open position to a fully closed position whereby the extendable boom is substantially parallel to the upright boom support and orthogonal to the ground. In the fully closed position ( FIGS. 1, 2 and 6 ), the extendable boom is nestable within the spaced apart upright support arms 22 a , 22 b.
  • FIGS. 7 ( a ) to 7 ( g ) inclusive there is shown a number of side views of the forklift truck in operation.
  • the forklift trucks lifting assembly carriage is in a fully aft position on the side plates 7 and extension ram 39 is extended so that the lifting forks 27 are located adjacent the ground between the two side plates 7 .
  • a load shown here as a pallet of bricks, may be lifted between the side plates 7 for maximum stability.
  • FIG. 7 ( b ) the load is raised off the ground by retraction of the extension ram 39 to its fully retracted position, the load may then be transported to its desired destination in this configuration.
  • the load is lifted upwards further by pivoting the extendable boom 23 by manipulation of the lift rams 31 , 33 , which may be operated until the extendable boom is in a fully open position with the boom facing upwardly and away from the boom support as seen in FIG. 7 ( c ).
  • the boom is then extended by operation of the extension ram 39 until in a fully extended position as seen in FIG. 7 ( d ) whereafter the load may be deposited in the desired location.
  • stabilizers (not shown) will be provided on the forklift which may be deployed at appropriate times to prevent overbalancing of the forklift during loading and unloading operations. This will be almost certainly necessary when attempting maximum reach with heavy loads on the forks.
  • the nature of the stabilizers and their deployment would be readily understood by the person skilled in the art and will not be discussed further in this application.
  • FIGS. 8 ( a ) to 8 ( d ) inclusive there is shown the sequential steps in mounting a truck mounted forklift 1 according to the invention onto the rear of a carrying vehicle 41 .
  • the truck mounted forklift has its carriage in a substantially forward position with respect to the side plates and the boom is in a retracted although not necessarily fully retracted position.
  • the lifting forks 27 are inserted into specially adapted fork receiving sockets 43 mounted on the undercarriage of the carrying vehicle 41 until the heel of the lifting forks bear against the entrance of the sockets. Once the lifting forks are fully inserted into the sockets ( FIG.
  • the operator of the vehicle causes a manual tilt of the forks via an appropriate tilt mechanism to tilt the forks upwards which will cause the upper portion of the forklift to lean inwardly with respect to the carrying vehicle.
  • the extension ram 39 is then operated to extend the boom which causes the piggyback forklift to rise off the ground ( FIG. 8 ( c )).
  • the means to move the carriage forwards and backwards along the chassis relative to the rear crossbar is operated to move the carriage to a fully aft position relative the rear crossbar.
  • This in turn will cause the rest of the piggyback forklift to move forwards relative the carrying vehicle until the wheels and part of the side plates 7 are located underneath the undercarriage of the carrying vehicle, as shown in FIG. 8 ( d ).
  • the wheels 9 will rest on steps 45 .
  • Additional locking members may be provided to secure the forklift in position relative the carrying vehicle.
  • the mounting movement of the piggyback forklift onto the carrying vehicle is practically vertical as opposed to the known telescopic boom devices in which the piggyback forklift would be lifted in an arcuate path onto the carrying vehicle which can cause wear and tear to the lifting components. Furthermore, the operator may remain in the vehicle at all times during the mounting dismounting process.
  • FIGS. 9 and 10 there is shown the piggyback forklift truck according to the invention in operation unloading goods from a flatbed truck.
  • the boom may be fully extended and the carriage moved to a forwardmost position relative the sidearms to allow a “far side” load to be collected by the forklift. No additional rollers or pantograph system is required to reach the far side of the flatbed truck.
  • FIGS. 11 and 12 there is shown a pair of perspective views of the lifting assembly 17 for use with the piggyback forklift according to the invention.
  • the lifting assembly 17 comprises a carriage 19 upon which there is mounted a vertical boom support 21 projecting upwardly therefrom.
  • An extendible boom 23 comprising an outer casing 35 and an inner casing 37 is pivotally mounted adjacent the upper part of the boom support.
  • the inner casing 37 is slidably mounted inside the outer casing 35 which is in turn pivotally mounted on the boom support.
  • a pair of lift rams 31 , 33 are provided to pivot the boom relative the boom support about its mounting and an extension ram 39 is provided to extend and retract the inner casing of the boom relative the outer casing.
  • One of said lift rams is a high pressure lift ram capable of withstanding pressures up to 450 bar while the other is a low pressure ram capable of withstanding pressures of up to 330 bar.
  • Rollers 51 are provided on the carriage for engagement in the tracks (not shown) of the side plates.
  • means to move the carriage back and forth along the chassis provided by a ram 52 connected at one end to the carriage 19 and at its other end to the chassis (not shown). Operation of the ram 52 will cause the carriage to move on the rollers 51 in the tracks forwards and backwards on the chassis relative the rear crossbar.
  • FIG. 13 there is shown a cross-sectional side view of the lifting assembly shown in FIGS. 11 and 12 .
  • the lifting assembly further comprises a compensation jack 53 and a linkage mechanism 55 which will be described in greater detail below.
  • the compensating jack is connected at one of its ends to the boom and connected at its other end to the fork carrier via the linkage mechanism and further comprises a back-to-back duplex ram comprising a compensating jack ram 57 and a controllable tilt ram 59 .
  • the compensating jack ram 57 is responsive to the orientation of the boom and operable on the fork carrier to maintain the forks in a fixed orientation with respect to the ground during raising or lowering of the boom.
  • the controllable tilt ram 59 is operable as a controllable tilt for manipulation by the operator of the forklift to manually tilt the forks by a predetermined amount.
  • the fluid supply of the compensating jack ram is sequenced with the fluid supply of the high pressure lift ram 31 so that as the fluid supply in the high pressure lift ram changes as the boom is raised or lowered so too will the fluid supply to the compensating jack ram change.
  • the fluid supply to the compensating jack ram is inversely proportional to the fluid supply to the high pressure lift ram.
  • the lifting rams 31 , 33 are extended by pumping fluid into the cylinder bore (not shown) of the low pressure lift ram and the rod-end of the compensation ram where the bore of the compensation ram feeds directly into the bore of the high pressure lift ram.
  • This causes the boom to pivot about its mounting point 61 on the boom support.
  • fluid is drawn from the cylinder bore 63 of the compensating jack ram which may be fed to the high pressure lift ram 31 by way of a hydraulic circuit, not shown.
  • the piston 65 will retreat into the cylinder bore acting also under the weight of the forks 27 and fork carrier 25 .
  • the forks and fork carrier will pivot clockwise (in the orientation shown) about pivot point 69 connecting the fork carrier to the boom, this will cause the forks to remain in a fixed orientation with the ground as the boom is being raised.
  • the controllable tilt ram 59 comprises a piston 75 mounted in a tilt ram cylinder bore 77 .
  • the piston is attached at one end to the boom.
  • the controllable tilt ram 59 has a cylinder bore diameter greater than that of the compensating jack ram.
  • the operator of a vehicle may decide to provide a downward pre-tilt to the forks when dropping off goods or an upward pre-tilt to the forks once they have been engaged and are to be transported.
  • fluid is either delivered to or drawn off from the tilt ram cylinder bore.
  • This causes the entire compensating jack to move towards or away from the end of the boom remote from the fork carrier as the amount of fluid in the compensating jack ram cylinder bore will remain constant unless the boom is also being moved at that time.
  • This in turn will act on the link mechanism to cause the forks to rotate about pivot point 69 . In this way, the operator may essentially cause the forks to rotate so that they are no longer parallel to the ground and are tilting upwards or downwards as required.
  • the compensating ram will keep the forks in a fixed orientation with the ground.
  • the position of the forks relative the boom will be altered by the compensating ram in response to upwards or downwards movement of the entire boom caused by the lifting ram but the forks will maintain their orientation with the ground throughout. Only when the tilt ram is adjusted will the forks orientation with the ground be altered.
  • the tilt ram can therefore be used to effectively override the compensating ram if need be although the tilt ram is only adjustable to a very small degree compared with the compensating ram as the stroke of the tilt ram is significantly less than the stroke of the compensating ram.
  • the linkage mechanism 55 of the present invention in greater detail compared with a known linkage mechanism.
  • the linkage mechanism further comprises a first link member 81 pivotally mounted at its ends to the compensating jack ram piston 65 at one end and the fork carrier 25 at its other end and a second link member 83 pivotally mounted to the compensating jack ram piston 65 at one of its ends and the extendible boom 23 at its other end to spread the loading on the compensating ram and redirect the forces acting on the compensating ram.
  • the second link member 83 is arcuate in shape.
  • the angle between the direction of force applied by the forks, indicated by the arrow R 1 and R 3 , and the longitudinal axis of the compensating jack is sufficiently small regardless of whether or not the forks are perpendicular to the longitudinal axis of the boom such as when the boom is fully lowered, or when the forks are substantially parallel to the longitudinal axis of the boom such as when the boom is fully raised.
  • This enables the compensating ram to provide an equal but opposite force and provide tilt to the forks when necessary.
  • the angle described may be kept relatively small at all times. By keeping the angle small at all times, the pressures exerted on the forks are not excessive and therefore continuous operation of the compensation jack can be obtained with a less heavy duty compensation jack.
  • FIGS. 15 ( a ) and 15 ( b ) a standard solid bracket is substituted for the link mechanism. It can be seen that the angle between the direction of force R 2 and the longitudinal axis of the compensating jack is virtually identical to the angle between the direction of force R 1 and the longitudinal axis of the compensating jack for the link mechanism when the forks are substantially perpendicular to the longitudinal axis of the boom. However, when the boom is raised and the forks are substantially parallel to the longitudinal axis of the boom, the angle between the position and direction of force R 4 and the longitudinal axis of the compensating jack is far greater than the angle between the direction of force R 3 and the longitudinal axis of the compensating jack for the link mechanism.
  • the forks were described as being substantially parallel to the longitudinal axis of the boom. In fact the forks would have turned through an angle of in the region of 110° from their position perpendicular to the longitudinal axis of the boom so would have passed through the parallel and are in fact angled 20° beyond parallel. It is important to note that the forks are shown in their neutral position and a further ⁇ 8° of tilt could be applied by the operator thereby further rotating the fork clockwise which would create an even larger angle for the known systems.
  • the link mechanism described can therefore cut down significantly the size of compensating jack that is required.
  • FIG. 16 ( a ) to FIG. 16 ( d ) inclusive there is shown a schematic representation of the hydraulic rams operable on the lifting assembly, where like parts have been given the same reference numeral as before, including the compensating jack ram 57 and controllable tilt ram 59 connected to the forks 27 via fork carrier (not shown), as well as the lift rams 31 , 33 connected to the boom (not shown).
  • the compensating jack ram further comprises a compensating jack ram phasing valve 91 and the high pressure lift ram 31 further comprises a boom supporter cylinder phasing valve 93 .
  • Control of the lifting and lowering of the extendible boom is carried out through controller 95 and associated boom valve 97 whereas control of the adjustment of the controllable tilt ram 59 is carried out through tilt controller 99 and associated tilt cylinder 101 .
  • compensation valve 103 There is further provided compensation valve 103 .
  • fluid is delivered to or drawn from the various cylinders in the manner shown by the arrows. Fluid is delivered to cylinder bore 107 of low-pressure lift ram 33 and to cylinder rod-end 71 of the compensation ram 57 .
  • the cylinder bore of this cylinder feeds directly into the cylinder bore 105 of the high-pressure lift ram 31 .
  • the pressure generated in cylinder bore 105 of the high-pressure lift ram 31 is the cumulative sum of the pressure caused by the fluid feed into rod-end 57 and the induced pressure caused by the loading of the forks 27 .
  • the boom also employs a reset function to allow an operator to realign the high-pressure lift ram 31 and the compensation ram 57 .
  • This is achieved by manner of valves 91 and 93 which are installed in the piston heads of compensation ram 57 and the high-pressure lift ram 31 respectively. These valves allow free flow through the piston head when the respective cylinders are in the closed position.
  • This reset function can only be preformed under unloaded conditions. These valves do not allow for free flow of oil in conditions which would cause the boom to lower.
  • an operator would be required to close the boom mechanism fully and apply pressure for 5 seconds. This applies pressure to cylinder rod-ends 109 and 111 of the high-pressure lift ram 31 and the low-pressure lift ram 33 respectively.
  • the valve in the piston head of the high-pressure lift ram 31 would allow free flow from the rod-end 31 to the bore end 105 of this cylinder and subsequently would extend the compensation ram 57 to the fully open position thus realigning the rams.
  • the operator would also be required to open the boom mechanism fully and apply pressure for 5 seconds. This applies pressure to the cylinder rod-end 57 of the compensation ram 57 .
  • the compensation ram 57 would reach its closed position before the high-pressure lift ram 31 .
  • the valve in the piston head of the compensation ram 57 would then allow free flow from cylinder rod-end 57 to cylinder bore 63 and subsequently would extend the high-pressure lift ram 31 to its fully open position thus fully realigning the rams.
  • FIG. 17 of the drawings there is shown a stability triangle diagram of the forklift according to the present invention compared with a typical boom design forklift.
  • the centre of gravity of the machine is close to the back wheel of the machine. This means that the distance between the centre of gravity and the side of the stability triangle will be quite small (indicated as X in the diagram). With the centre of gravity being so close to the stability triangle side the machine will be less stable.
  • the centre of gravity will be moved forwards on the machine further away from the back wheel. This will cause the distance of the centre of gravity to the side of the stability triangle (indicated as X 1 in the diagram) to be increased thereby increasing the stability of the machine.
  • the positions shown are for forklifts that are not loaded. The range of tilt possible while maintaining stability is much greater for the truck mounted forklift according to the invention.
  • the extendible boom is described as a two part boom with an outer casing and an inner casing that slides relative the outer casing. It will be understood that by extendible in this case it may not necessarily mean the boom that is extendible in length but rather the boom which is extendible in reach. Instead of the two part boom it is envisaged that a telescopic extendible boom could also be provided in which at least one boom support section is nested within another boom support section and will allow extension of the boom thereby extending the reach of the boom. The telescopic boom is also therefore an extendable boom within the meaning of the specification.
  • the fluid supply of the high pressure lift ram may be sequenced with the compensating jack ram. It is envisaged that there may be provided a fluid connector between the cylinder bore of the compensating ram and the cylinder bore of the lifting ram with a series of valves. On the forks having a load placed thereon, additional pressure will be induced onto the fluid contained in the compensating ram cylinder bore by virtue of the fact that the weight of the load on the forks will tend to push the piston inwardly into the cylinder bore. The additional pressure build up can then be transferred to the cylinder bore of the high pressure lift ram by way of the fluid connector and series of valves to assist in the lifting of the boom.
  • the section of the boom is shown to be hexagonal in cross-section.
  • the boom could in fact be square in cross section. It is envisaged that instead of being directly perpendicular to the ground the boom could be at an angle of between ⁇ 10° of the orthogonal with respect to the ground. This is sufficient to obtain the main advantages from the invention.
  • the fork carrier could be provided with a shift mechanism to allow sideways movement of the forks relative the fork carrier. This will allow adjustment of the forks without having to readjust the position of the forklift.
  • the linkage mechanism has been described in relation to piggyback forklifts only.
  • linkage mechanism could also be used in connection with many other different types of pivoting booms and not solely with the pivoting extendable booms described.
  • the linkage mechanism is in no way restricted to use solely with truck mounted forklifts and could find applications in other types of forklift and industrial machinery.
  • the linkage mechanism could be used in connection with other end attachments such as a bucket or other arrangement and is not restricted solely to use with the forks described above.
  • the linkage mechanism would work equally well on larger or smaller scale machines including but not limited to forklifts where there is a pivoting member that is being caused to pivot under the action of a ram.
  • link arms could both be straight or one or both could be arcuate in shape.

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mechanical Engineering (AREA)
  • Forklifts And Lifting Vehicles (AREA)
  • Pallets (AREA)
  • De-Stacking Of Articles (AREA)
US10/989,552 2003-11-17 2004-11-17 Forklifts Abandoned US20050220588A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IE20030859 2003-11-17
IES2003-0859 2003-11-17

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US20050220588A1 true US20050220588A1 (en) 2005-10-06

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US10/989,552 Abandoned US20050220588A1 (en) 2003-11-17 2004-11-17 Forklifts

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US (1) US20050220588A1 (de)
EP (1) EP1531141B1 (de)
AT (1) ATE335703T1 (de)
DE (1) DE602004001836T2 (de)
ES (1) ES2271763T3 (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060180514A1 (en) * 2004-10-23 2006-08-17 Martin Thomas L Jr Material catching, repositioning, and waste reducing apparatus with tilt capability
US7255202B2 (en) * 2003-05-30 2007-08-14 Moffett Research And Development Limited Truck mounted forklift with double-acting freelift mast
US20090145696A1 (en) * 2007-12-06 2009-06-11 Jungheinrich Aktiengesellschaft Three-Wheeled Vehicle, in Particular Industrial Truck Comprising A Stabilizing Device
US8078368B2 (en) 2010-05-01 2011-12-13 Walter Hall Lift truck safety system
US20130006444A1 (en) * 2011-07-01 2013-01-03 Cardinal Gibbons High School Folding Forklift
WO2017064313A1 (en) * 2015-10-14 2017-04-20 Cargotec Research & Development Ireland Limited A truck mounted forklift
US10315853B2 (en) 2015-08-10 2019-06-11 Superior Industries, Inc. Conveyor leveling systems and methods
US10412900B2 (en) * 2017-04-28 2019-09-17 Progress Rail Services Corporation Implement System for a machine
CN110482447A (zh) * 2019-08-20 2019-11-22 戚春凤 一种适用于叉车的侧面货叉机构
US20210331906A1 (en) * 2020-04-24 2021-10-28 Cargotec Engineering Ireland Limited Truck mounted forklift

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008147218A2 (en) * 2007-05-30 2008-12-04 Olav Lauvdal Forklift truck and method for transporting a forklift truck
GB2575825B (en) * 2018-07-24 2022-04-20 Cargotec Res & Development Ireland Limited A truck mounted forklift
IT202000025180A1 (it) * 2020-10-23 2022-04-23 Manitou Italia Srl Portaforche perfezionato
CN113955677B (zh) * 2021-09-22 2023-02-28 江西省农业科学院畜牧兽医研究所 一种生猪养殖用转运装置

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US4826474A (en) * 1987-12-14 1989-05-02 Butterworth Jetting Systems, Inc. Forklift apparatus for unloading articles from an elevated surface
US5494395A (en) * 1991-01-08 1996-02-27 Raunisto; Yrjoe Driving machine with an articulated boom
US5328321A (en) * 1991-09-05 1994-07-12 Moffett Research And Development Limited Multi-stage mast for a forklift truck
US5480275A (en) * 1993-10-18 1996-01-02 Taylor Iron-Machine Works, Inc. Fork lift truck
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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7255202B2 (en) * 2003-05-30 2007-08-14 Moffett Research And Development Limited Truck mounted forklift with double-acting freelift mast
US20060180514A1 (en) * 2004-10-23 2006-08-17 Martin Thomas L Jr Material catching, repositioning, and waste reducing apparatus with tilt capability
US20090145696A1 (en) * 2007-12-06 2009-06-11 Jungheinrich Aktiengesellschaft Three-Wheeled Vehicle, in Particular Industrial Truck Comprising A Stabilizing Device
US7967335B2 (en) * 2007-12-06 2011-06-28 Jungheinrich Aktiengesellschaft Three-wheeled vehicle, in particular industrial truck comprising a stabilizing device
US8078368B2 (en) 2010-05-01 2011-12-13 Walter Hall Lift truck safety system
US20110308889A1 (en) * 2010-05-01 2011-12-22 Hall Walter D Lift Truck Safety System With Pivoting Fork
US20130006444A1 (en) * 2011-07-01 2013-01-03 Cardinal Gibbons High School Folding Forklift
US8794386B2 (en) * 2011-07-01 2014-08-05 Cardinal Gibbons High School Folding forklift
US10315853B2 (en) 2015-08-10 2019-06-11 Superior Industries, Inc. Conveyor leveling systems and methods
WO2017064313A1 (en) * 2015-10-14 2017-04-20 Cargotec Research & Development Ireland Limited A truck mounted forklift
US20180319639A1 (en) * 2015-10-14 2018-11-08 Cargotec Research & Development Ireland Limited A truck mounted forklift
US11167965B2 (en) 2015-10-14 2021-11-09 Cargotec Research & Development Ireland Limited Truck mounted forklift
US10412900B2 (en) * 2017-04-28 2019-09-17 Progress Rail Services Corporation Implement System for a machine
CN110482447A (zh) * 2019-08-20 2019-11-22 戚春凤 一种适用于叉车的侧面货叉机构
US20210331906A1 (en) * 2020-04-24 2021-10-28 Cargotec Engineering Ireland Limited Truck mounted forklift

Also Published As

Publication number Publication date
ATE335703T1 (de) 2006-09-15
EP1531141B1 (de) 2006-08-09
DE602004001836D1 (de) 2006-09-21
ES2271763T3 (es) 2007-04-16
EP1531141A1 (de) 2005-05-18
DE602004001836T2 (de) 2007-03-29

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